In the theory of common prosperity, two conceptions of justice, namely that of need and equality, are intertwinedUnder different conceptions of justice, the theoretical scenario, major tasks, and practice modes are fundamentally differentFor the justice of need, the essential aspect of common prosperity is the satisfaction of basic needs and the continuous improvement and perfection of those conditions leading to a better lifeLiberating and developing productivity and promoting social production are always the premise and foundation for the justice of needAs for the justice of equality, the focus of common prosperity is the sharing of social developments and preventing polarization; a fair mode and a fair structure of distribution are the core of this theoryThese two conceptions of justice do not necessarily conflict with each other, yet the question on which of the two should be given the theoretical priority and urgency of practice reveals a predominant difference about the cognition and solutions of common prosperity under different historical stages Currently, basic need for a better life constitutes the priority for the theoretical construction and practice of the principle of justice.